The invention concerns an electromechanical actuator with which one can adjust the turbocharger of internal combustion engines.
It is known that turbochargers for internal combustion engines need a regulating apparatus to regulate the exit pressure of the compressor.
Said apparatus is activated by an actuator controlled by the engine's electronic control unit (ECU), or by another equivalent system. The aim is to supply the necessary power to move or maintain the turbocharger's regulation levers in the correct position. To maximize the efficiency of the turbocharger at each change of the engine's operational regime, it is indispensable that the regulation of the exit pressure of the compressor be the quickest and most precise possible, with reference to the signals from the ECU or any other equivalent electronic system, hereinafter called for simplicity's sake electronic control unit.
Independently from the way in which the compressor's exit pressure has charged, therefore either in the “waste gate” type of solution, or in the solution in which the inclination of the turbine's stator blade (variable geometry turbocharger), said adjustments are normally carried out through the linear sliding, or nearly linear, of a pivot point.
At the present state of the art the most common systems for the carrying out of the regulation of the turbocharger are two:
the first is a pneumatic type and it covers about 99% of the applications;
the second, called REA (Rotatory Electric Actuator), the object of the U.S. Pat. No. 6,360,541B2, is of the electric type.
The pneumatic type actuator, the first type, is composed of a single effect jack—comprising a sealed chamber, a membrane and a piston with a spring—which functions in compression or in depression.
The control of the turbocharger by the engine's electronic control unit is indirect or may be even absent when in the turbochargers with connection and pressure catch directly from the crankcase of the compressor.
In fact the signal transmitted by th engine's electronic control unit inflects an electric valve which, by acting on a constant pressure tank, adjusts the pressure or depression values that must reach the actuator which, consequently, controls the pivot point. Said system, although relatively economical, carries the following disadvantages:
it is imprecise due to the plurality of levers and of the non negligible relevance of the internal frictions which also determine a hysteresis of the same system;
it is slow, due to the pneumatic activation, therefore, when there are sudden changes in the engine's regimen, the fluid dynamic transients constrain the system's responsene capacity;
it requires a dedicated pneumatic system with connectors, tank and regulation electro-valve which change with the change of the engine on which said actuator is applied.
The REA type actuator, the second type, comprises an electric motor and a speed reduction group with a rotating exit. The control system interacts with a plurality of sensors among which the exhaust gas recirculation system (EGR) to co-ordinate the operations of the turbocharger with those of the engine and the EGR.
Said REA type actuator therefore:
requires an electric motor with reduction group which limits its speed and increases the exit torque to make it appropriate for controlling the pivot point;
it needs a plurality of control connections which require specific adjustments for its use with different engines;
it moves into the “hot spot” the electronics related to a series of activities which, in other types of actuators, are normally carried out by the engine's electronic control unit;
it is rather complex and therefore costly.